Precision microwave frequency synthesizer and receiver with delay balanced drift canceling loop

ABSTRACT

An example frequency converter includes a drift canceling loop with a balanced delay and a linear signal path (e.g., linear with respect to frequency scaling, amplitude modulation, and/or phase modulation). One side of the drift canceling loop includes a fixed delay, and the opposite side includes an adjustable, complementary delay. The adjustable, complementary delay facilitates precision matching of the signal delays on each side of the loop over a range of frequencies, which results in a significant improvement in noise cancellation, particularly at large offsets to the carrier, while permitting the use of a higher noise, but very fast tuning course scale oscillator. The linear signal path from the signal generator to an RF output facilitates modulation of the signal by the signal generator. A modular format is an advantageous embodiment of the invention that includes the removal of the frequency synthesizer&#39;s low phase noise reference into a separate module.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/636,515, filed on Jun. 28, 2017 by at least one common inventor,which claims the right of priority to co-pending U.S. Provisional PatentApplication No. 62/355,553, filed on Jun. 28, 2016 by at least onecommon inventor, both of which are incorporated herein by reference intheir entireties.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates generally to frequency synthesizers andreceivers, and more particularly to frequency synthesizers and receiversin the microwave region.

Description of the Background Art

Frequency synthesizers using noise or drift canceling loops are wellknown for providing low phase noise and short phase & frequency settlingtimes. However, known synthesizers have been found unsuitable for manyapplications, such as threat simulation and radar target generation, dueto their failure to provide satisfactory signal modulation within thegenerator and their lack of phase coherent frequency switchingcharacteristics. In other applications, phase stability across multiplefrequency synthesizers is important. For example, long term phasestability between channels is required to calibrate direction findingequipment that must operate at great distances. Known synthesizerstypically have not adequately addressed situations that require thecoordination of multiple channels.

SUMMARY

The present invention overcomes the problems associated with the priorart by providing a frequency synthesizer that is operable in themicrowave region and provides significant signal modulation capabilityin the synthesizer. The synthesizer exhibits low phase noise, is finelytunable (e.g., 1 Hz step size) and can switch frequency in a phasecoherent manner within 500 nano-seconds (nsec) or less. The inventionfacilitates the effective simulation of radar signals for use in testingthe effectiveness of radar countermeasure equipment, for generatingradar targets for evaluating the radar's resistance to jamming and forcalibrating direction finding systems.

An example frequency synthesizer (up-converter) includes a driftcanceling loop with a balanced delay and a linear signal path (e.g.,linear with respect to frequency scaling, amplitude modulation, and/orphase modulation). In particular, one side of the drift canceling loopincludes a fixed delay, and the opposite side of the drift cancelingloop includes an adjustable, complementary delay. The adjustable,complementary delay facilitates precision matching of the signal delayson each side of the loop over a range of frequencies, which results in asignificant improvement in noise cancellation, particularly at largeoffsets to the carrier while permitting the use of a higher noise, butvery fast tuning course scale oscillator. The linear signal path fromthe signal generator to an RF output facilitates modulation of thesignal by the signal generator. A modular format is considered anadvantageous embodiment of the invention, which includes the removal ofthe frequency synthesizer's low phase noise reference into a separatemodule.

An example receiver (down-converter) including a drift canceling loopwith a balanced delay and a linear signal path is also disclosed.

An example signal converter includes a first mixer, a second mixer, avariable oscillator, a splitter, a delay device, and a complementarydelay device. The first mixer includes an input for receiving a signalto be converted, and the second mixer includes an output for providingthe converted signal. The variable oscillator produces a signal (CS)variable at a first scale (e.g., frequency step resolution). Thesplitter is coupled to the first mixer and the second mixer to form adrift canceling loop. The splitter includes an input coupled to receivethe signal (CS) from the variable oscillator, a first output coupled tointroduce the signal (CS) into the drift canceling loop along a firstdirection, and a second output coupled to introduce the signal (CS) intothe drift canceling loop along a second direction opposite the firstdirection. The delay device is coupled between the second output of thesplitter and an input of the second mixer, and a complementary delaydevice is coupled between the first output of the splitter and an inputof the first mixer. At least one of the delay device and thecomplementary delay device is adjustable. In one example embodiment, thesignal received by the first mixer is downconverted. In another exampleembodiment, the signal received by the first mixer is upconverted.

In a disclosed embodiment, the signal path from the input of the firstmixer to the output of the second mixer is linear (e.g., linear withrespect to frequency scaling, amplitude modulation, and/or phasemodulation).

The example signal converter further includes a second variableoscillator and a third mixer. The second variable oscillator produces asignal (FS) variable at a second scale finer than the first scale (e.g.,finer step-wise adjustment of frequency). The third mixer is coupledbetween the splitter and the first mixer and has an input coupled toreceive the signal (FS) from the second variable oscillator.

In a particular embodiment, the complementary delay device introduces anadjustable delay to signals passing therethrough, and the delay deviceintroduces a fixed delay to signals passing therethrough. The delaydevice introduces a delay in one side of the drift canceling loop thatexceeds by a predetermined amount a delay that would occur in anopposite side of the drift canceling loop without the complementarydelay device. The complementary delay device is adjustable over a rangesufficient to balance the delays on both sides of the drift cancelingloop for a predetermined range of signal frequencies. A controller iscoupled to the complementary delay device and is operative to adjust thecomplementary delay device based at least in part on a current frequencyof the variable oscillator and a current frequency of the secondvariable oscillator.

The example signal converter optionally includes a slave output and asecond slave output. The slave output is coupled to provide a signal(LO1) from a second input of the first mixer to a slave converter. Thesecond slave output is coupled to provide a signal (LO2) from an inputof the second mixer to the slave converter.

An example slave converter includes a first mixer and a second mixer,but does not include a drift canceling loop. Instead, the first mixerincludes an input for receiving a second signal to be converted and asecond input coupled to the slave output. The second mixer includes anoutput for providing the converted second signal and an input coupled tothe second slave output.

Optionally, the signal converter can include a plurality of the slaveconverters. Each of the slave converters includes a first mixer and asecond mixer, but does not include a drift canceling loop. Instead, thefirst mixer includes an input for receiving a respective signal to beconverted and a second input coupled to receive the signal (LO1) fromthe slave output of the master portion of the signal converter. Thesecond mixer includes an output for providing the respective convertedsignal and an input coupled to receive the signal (LO2) from the secondslave output of the master portion of the signal converter.

An example modular converter system is also disclosed. The examplemodular system includes a mounting structure adapted to receive one ormore master converter modules and one or more slave converter modules.The system further includes a reference signal generator, referenceconnectors, slave connectors, a data interface, and a control interface.The reference signal generator is mountable in the mounting structure(e.g., housing, cabinet, rack, etc.) and operable to generate at leastone reference signal (R2). The reference connectors are disposed in themounting structure and coupled to provide the at least one referencesignal (R2) to any master converter modules present in the mountingstructure. The slave connectors are coupled to provide slave signalsfrom the one or more master converter modules to associated ones of theone or more slave control modules. The data interface is operative tocommunicate signals to be converted to the one or more master convertersand to the one or more slave converters. The control interface isoperative to communicate frequency control signals to the one or moremaster converter modules.

The modular converter system can include one or more of the masterconverter modules, each the master converter module including a mastersignal converter. Each master signal converter includes a first mixer, asecond mixer, a variable oscillator, a splitter, a second variableoscillator, a third mixer, a slave output and a second slave output. Thefirst mixer includes an input coupled to the data interface forreceiving a signal to be converted. The second mixer includes an outputfor providing the converted signal. The variable oscillator produces asignal (CS) variable at a first scale (e.g., frequency step resolution).The splitter is coupled to the first mixer and the second mixer to forma drift canceling loop. The splitter includes an input coupled toreceive the signal (CS) from the variable oscillator, a first outputcoupled to introduce the signal (CS) into the drift canceling loop alonga first direction, and a second output coupled to introduce the signal(CS) into the drift canceling loop along a second direction opposite thefirst direction. The second variable oscillator is coupled to receivethe reference signal (R2) via the reference connectors and is operativeto produce a signal (FS) variable at a second scale, finer than thefirst scale, depending on the reference signal (R2). The third mixer iscoupled between the splitter and the first mixer and has an inputcoupled to receive the signal (FS) from the second variable oscillator.The slave output is coupled to provide a slave signal (LO1) from asecond input of the first mixer (to a slave module) via one of the slaveconnectors, and the second slave output is coupled to provide a secondslave signal (LO2) from an input of the second mixer (to the same slavemodule) via another of the slave connectors.

The example modular converter system additionally includes one or moreof the slave converter modules, each the slave converter moduleincluding a slave signal converter. Each slave signal converter includesa first mixer and a second mixer, but not a drift canceling loop. Thefirst mixer includes an input for receiving an associated signal to beconverted and a second input coupled to receive a slave signal (LO1) viaan associated one of the slave connectors. The second mixer includes anoutput for providing the converted second signal and an input coupled toreceive a second slave signal (LO2) via another associated one of theslave connectors. Optionally, each slave converter module can include aplurality of the slave signal converters.

In an even more particular embodiment, the reference signal generator isoperative to generate another reference signal (R1), and the referenceconnectors are coupled to provide the reference signal (R1) to anymaster converter modules present in the mounting structure. In addition,each master signal converter includes a fourth mixer and a harmonicgenerator. The fourth mixer is coupled between the splitter and thethird mixer. The harmonic generator has an input coupled to receive thereference signal (R1), via an associated one of the referenceconnectors, and has an output coupled to an input of the fourth mixer.The electrical path length of every said reference connectorcommunicating said reference signal (R1) is the same, and the electricalpath length of every said reference connector communicating saidreference signal (R2) is the same. Optionally, the electrical pathlength of every said reference connector communicating said referencesignals (R1) and (R2) is the same.

In an example modular converter system, the master signal converteradditionally includes a delay device and a complementary delay device.The delay device is coupled between the second output of the splitterand an input of the second mixer. The complementary delay device iscoupled between the first output of the splitter and an input of thefirst mixer. At least one of the delay device and the complementarydelay device is adjustable. In a particular embodiment, thecomplementary delay device is adjusted based at least in part on acurrent frequency of the variable oscillator and a current frequency ofthe second variable oscillator.

Optionally, one of the slave converter modules includes at least threeslave signal converters, one of the master converter module includes nomore than one master signal converter, and the slave converter module isno larger than the master converter module.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the followingdrawings, wherein like reference numbers denote substantially similarelements:

FIG. 1 is a block diagram of a master-slave system of synthesizers(up-converters) and/or receivers (down-converters);

FIG. 2 is a block diagram of an example synthesizer of FIG. 1;

FIG. 3 is a circuit diagram showing specific example components of thesynthesizer of FIG. 2;

FIG. 4 is a block diagram of the Fine Scale Variable Oscillator (FSVO)of FIGS. 2 and 3;

FIG. 5 is a block diagram of an example receiver of FIG. 1;

FIG. 6 is a circuit diagram showing specific example components of thereceiver of FIG. 5;

FIG. 7 is a block diagram of an example slave synthesizer of FIG. 1;

FIG. 8 is a block diagram of an example slave receiver of FIG. 1;

FIG. 9 is a block diagram of an alternate synthesizer; and

FIG. 10 is a block diagram of an alternate receiver.

DETAILED DESCRIPTION

The present invention overcomes the problems associated with the priorart, by providing a frequency converter (synthesizer or receiver) thatincludes a drift canceling loop with a balanced delay and a linearsignal path (e.g., in the up-converter). In the following description,numerous specific details are set forth (e.g., oscillator frequencies,filter frequencies, delay values, etc.) in order to provide a thoroughunderstanding of the invention. Those skilled in the art will recognize,however, that the invention may be practiced apart from these specificdetails. In other instances, details of well-known microwave synthesizercomponents, design, and use have been omitted, so as not tounnecessarily obscure the present invention.

Several aspects of the present invention will be apparent to thoseskilled in the art based on the content of the drawings, which alonewill enable a person of ordinary skill in the art to make and use thedisclosed inventions without undue experimentation. The drawings presentillustrative example embodiments, and should not be construed aslimiting the scope of the inventions. The following comments provideadditional clarification of some features and additional aspects of theinventions.

FIG. 1 is a block diagram of an example master-slave modular system ofsynthesizers/receivers 100. A plurality of master synthesizers/receivers102(1-N), a plurality of slave up/down-converters 104(1-M), and a commonreference 106 are coupled together to provide a plurality of coherent RFoutputs/inputs 108. In this example, one master circuit (e.g., a masterup-converter of FIG. 2 or FIG. 9, or a master down-converter of FIG. 4or FIG. 10) is included in each master module, and a plurality (e.g., 3)of slave up/down-converter circuits (e.g., the slave up-converter ofFIG. 7 or the slave down-converter of FIG. 8) is included in each slavemodule. In this example, all of master synthesizers 102(1-N) are drivenby the R1 and R2 reference signals provided by common reference 106, andslave up/down-converters 104(1-M) are driven by the LO1 and LO2 signalsprovided by master 102(N). However, each of masters 102(1-N) can drive aplurality of slave circuits 104(1-M), if desired.

Common reference 106 provides the R1 and R2 signals to each mastermodule 102(1-N) via a separate set of conductors 110(1-N) and 112(1-N),respectively (reference connectors). All of conductors 110(1-N)conveying the R1 signals from common reference 106 to master modules102(1-N) are of equal electrical length, and all of the conductors112(1-N) conveying the R2 signals from common reference 106 to mastermodules 102(1-N) are of equal electrical length. Optionally, theelectrical length of conductors 110(1-N) carrying the R1 signals is thesame as the electrical length of conductors 112(1-N) carrying the R2signals. The equal electrical length of conductors 110(1-N) and 112(1-N)carrying the R1 and R2 signals, respectively, ensures that any phasedrift (e.g., due to temperature change) in the RF outputs of the systemwill be the same and, therefore, the relative phases of the RF outputswill not change. In the example embodiment, equal length conductors areprovided in a mounting structure (e.g., rack/cabinet) 114, whereinmaster synthesizers/receivers 102(1-N) are also to be mounted.

Each of master synthesizers/receivers 102(1-N) and each slaveup/down-converter 104(1-M) receives a signal input from an associatedone of a plurality of signal generators/processors 116, which in thisexample embodiment are shown as separate components, but embodied withina general purpose computer system 118, along with a controller 120 and auser interface 122. Computer system 118 communicates with mastersynthesizers/receivers 102(1-N) and each slave up/down-converter104(1-M) via data and control interfaces (e.g. data and/or controlbusses) housed and coupled within the same rack/cabinet 114 as themaster modules 102(1-N) and slave modules 104(1-M). Alternatively,signal generators/processors 116 can be housed within a module mountablewithin rack/cabinet 114.

In this embodiment, all of master circuits 102(1-N) and slave circuits104(1-M) are shown as either up-converters or down converters. However,masters 102(1-N) and slaves 104(1-M) could all be down-converters or allup-converters. Indeed, any combination of master up-converters, masterdown-converters, slave up-converters, and/or slave down-converters couldbe used together depending on the needs of a particular application.

Calibration of a master converter (up or down) is accomplished bymeasuring the phase noise of the up-converter (or down-converter, with asuitable low-noise RF Input signal) for each variation of thecomplementary delay line at a given frequency. A local maxima issearched for within a given delay segment for a particular frequency.After data for all delay segments have been measured, the delay segmentwith the least amount of phase noise is selected as the nominalcomplementary delay for a given frequency. An array of this data is thenstored within controller 120 as calibration data. Complementary delaydata is not needed for slave converters 104(1-M), as slave converters104(1-M) take on the matched delay performance of the associated one ofmaster converters 102(1-N).

FIG. 2 is a block diagram of an example synthesizer (up-converter) 200,which includes the following components: a controller 202, a coursescale variable oscillator 204, a splitter 206, a delay circuit 208, acomplementary delay circuit 210, a harmonic generator 212, a first mixer(Mixer 1) 214, a first band-pass filter (BPF 1) 216, a fine scalevariable oscillator (FCVO) 218, a second mixer (Mixer 2) 220, a secondband-pass filter (BPF 2) 222, a linear mixer 224, a third band-passfilter (BPF 3) 226, a third mixer (Mixer 3) 228, and a low-pass filter(LPF) 230, all interconnected as shown in FIG. 2. The terminals of themixers are labeled to identify the local oscillator (LO) terminals, theintermediate frequency (IF) terminals, and the radio frequency (RF)terminals. In addition, small triangles are used to represent amplifiers232, which may be positioned between various components of examplefrequency generator 102.

User input (e.g., base frequency selection) is provided to controller202, which can be implemented with a field programmable gate array(FPGA), via controller 120 of system 100 (FIG. 1). Controller 120 caninclude, for example, a personal computer (PC) communicating withcontroller 202 via a high speed interface (e.g., PCIe). Responsive tothe user input, controller 202 provides a control signal to course scalevariable oscillator (CSVO) 204, which generates an output signal havinga frequency that depends on the control signal. Splitter 206 receivesthe output signal from CSVO 204, and communicates the signal to bothdelay circuit 208 and complementary delay circuit 210. Complementarydelay circuit 210 adds an adjustable delay to the signal, based on acontrol signal received from controller 202, and provides the delayedsignal to the LO terminal of first mixer 214. Delay circuit 208 adds afixed delay to the signal and provides the delayed signal to the LOterminal of third mixer 228. The relationship between the adjustabledelay of complementary delay 210 and the fixed delay of delay 208 willbe explained in greater detail below.

Harmonic Generator 212 and FSVO 218 receive reference frequency signals(R1 and R2, respectively) from common reference 106 and generate theiroutput based on the reference frequencies (R1 and R2). First mixer 214mixes the delayed signal with the output of harmonic generator 212 andprovides the resulting signal, through first band-pass filter 216, tothe LO terminal of second mixer 220. Second mixer 220 combines thefiltered signal with a signal from FSVO 218 and provides the combinedsignal, through second band-pass filter 222 to the LO terminal of linearmixer 224. Linear mixer 224 combines the signal provided to its LOterminal with a signal provided from one of signal generators 116 on itsIF terminal and provides the resulting signal, through third band-passfilter 226, to third mixer 228. Third mixer 228 combines the signal fromlinear mixer 224 with the delayed signal from delay circuit 208, tosubtract the original signal from CSVO 204, thereby canceling anyfrequency/phase drift of CSVO 204. The output of third mixer 228 isprovided to RF output 108 through a power amplifier 234 and low-passfilter 230.

FSVO 218 uses an arrangement employing a harmonic generator driven bythe R2 frequency reference signal, as will be described in greaterdetail below with reference to FIG. 4.

A linear path 236 from signal generator 116 to the RF output providesimportant advantages over the prior art. For example, the linear pathfacilitates/preserves amplitude, frequency and phase modulation of thesignal by/from signal generator 116. Signal generator 116 need operateonly over a range of frequencies that is much lower and narrower thanthe RF output signal, permitting the use of versatile digitaltechniques, such as FPGAs, deep memories and high speed digital toanalog converters to generate the IF input to linear mixer 224. Thelinear path, along with the flexibility of implementing signal generator116 using widely available digital techniques, permits generating highfidelity complex modulation waveforms at microwave frequencies. It isalso possible to generate the IF input to linear mixer 224 with similarfidelity using analog IQ techniques due to the modulator requiringbalance only over a narrow range of operation. The prior art thatemploys analog IQ modulation directly at the RF output will havedifficulty achieving the same level of signal fidelity due to the needto maintain balance of the modulator over the entire operating range ofthe synthesizer.

Similar advantages are available for the receiver (down-converter). Thelinear path maintains wide-bandwidths over a select few intermediatefrequencies, rather than requiring a plurality of block down-convertersthat are multiplexed together to cover a broad range of microwave inputfrequencies as is common in the present art. Using modern digitaltechniques, the output of the proposed receiver can then be convertedeither directly into a digital signal, or employ an IQ demodulator asdesired.

The relationship between the adjustable delay of complementary delay 210and the fixed delay of delay 208 also provides important advantages overthe prior art, by facilitating more precise control over the timing ofthe arrival of the signals at third mixer 228 and, therefore, morecomplete drift/noise cancellation. Complementary delay 210 may also beused to correct for frequency/phase fluctuations as a function oftemperature. The fixed delay is selected to exceed the expected delaycaused by the signal traversing the clockwise portion of thedrift-canceling loop, and complementary delay 210 is finely adjustableto facilitate precision balancing of the clockwise and counter-clockwisedelays. For example, in one embodiment, the expected delay caused by theclockwise portion of circuit 102 is determined to be about 5.0 nsec(5,000 psec), but the actual delay is frequency or temperaturedependent. Therefore, the delay is configured to be 5.5 nsec (5,500psec), and the complementary delay ranges from 250 psec to 750 psec andis adjustable in 50 psec increments, depending at least in part on thefrequency of the output of CSVO 204.

Common reference 106 can be on the same circuit board as frequencygenerator 200, or signals R1 and R2 can be provided from an externalsource, as shown in FIG. 1. When the R1 and R2 signals are providedseparately from shared between generators 116, harmonic generator 212and FSVO 218 within each synthesizer 102(1-N) is receiving the samesignal, which greatly enhances the phase stability between channels.

Signal generator 116 can be housed on the same circuit board or in thesame housing as frequency generator 200, but is more typically providedas a connected separate component.

Circuit 200, as shown in FIG. 2, is considered a master circuit, becauseit includes output terminals 238 and 240 to provide local oscillatorsignals (LO1 and LO2, respectively) to one or more slave circuits 104,such as, for example, the slave circuits shown in FIG. 7 and/or FIG. 8.

FIG. 3 is a circuit diagram showing specific, example components offrequency synthesizer 200 of FIG. 2. A 1 GHz crystal is included incommon reference 106 (FIG. 1), which provides the reference signals R1and R2, as shown. In this example embodiment, reference signal R1 is a 1GHz signal and reference signal R2 is a 200 MHz signal.

FIG. 4 is a circuit diagram showing FSVO 218 (FIG. 2). FSVO 218 uses anarrangement employing a harmonic generator 402 driven by the R2frequency reference signal to generate the LO signals for translatingthe output of a direct digital synthesizer (DDS) 404 into one of fivebands 406. FSVO 218 switches frequency in a phase coherent manner due tothe fact that the comb of frequencies produced by harmonic generator 402is always running and assuming DDS 404 switches in a phase coherentmanner. Although a typical DDS normally switches frequency in a phasecontinuous manner, it is well known how to make a DDS switch phasecoherently. Since the contribution of CSVO 204 is cancelled out in driftcancelling designs, the RF output switches in a phase coherent manner,because the comb of frequencies produced by harmonic generator 212(driven by the R1 frequency reference) is also always running.

FIG. 5 is a block diagram of an example receiver (down-converter) 500.Down-converter 500 is similar to up-converter 200, except that thelinear path 501 conducts an RF input signal in the opposite direction.

FIG. 6 is a circuit diagram showing specific, example components ofreceiver 500.

FIG. 7 is a block diagram of an example slave up-converter 700. Slaveup-converter 700 includes a linear path similar to master synthesizer200 of FIG. 2, but not the remainder of the noise/drift canceling loop.Instead, slave up-converter 700 includes input terminals 702 and 704 forreceiving the LO1 and LO2 signals, respectively from a master circuit102 or another slave circuit 104. Sharing the LO1 and LO2 signalsbetween slave units 104 has the effect of sharing the master unit'sharmonic generator, which delivers a significant improvement in shortterm phase stability between a master unit and its slave channels. Theother master or slave circuit can be an up-converter circuit or adown-converter circuit. Slave up-converter 700 also includes outputterminals 706 and 708 for providing the LO1 and LO2 signals,respectively, to another one of slave circuits (up-converter ordown-converter) 104.

FIG. 8 is a block diagram of an example slave receiver (down-converter)800. Slave receiver 800 includes a linear path similar to the masterreceiver of FIG. 5, but not the remainder of the noise/drift cancelingloop. Instead, slave receiver 800 includes input terminals 802 and 804for receiving the LO1 and LO2 signals, respectively, from a mastercircuit 102 or another slave circuit 104. The other master or slavecircuit can be an up-converter circuit or a down-converter circuit.Slave receiver 800 also includes output terminals 806 and 808 forproviding the LO1 and LO2 signals, respectively, to another one of slavecircuits (up-converter or down-converter) 104.

FIG. 9 is a block diagram of an alternate synthesizer (up-converter)900. The alternate synthesizer of FIG. 9 is similar to frequencysynthesizer 200 of FIG. 2, except that a complementary delay 910 isinterposed between a first band-pass filter 916 and a second mixer 920.Disposing complementary delay 910 after first band-pass filter 916provides an advantage because complementary delay 910 can be frequencydependent and is, therefore, more precisely controllable for a narrowband of frequencies provided by first band-pass filter 916. However,complementary delay 910 can be effected anywhere between a splitter 906and a linear mixer 924.

FIG. 10 is a block diagram of an alternate receiver (down-converter)1000. The down-converter of FIG. 10 is similar to the up-converter ofFIG. 9, except that the linear path conducts an RF input signal in theopposite direction.

The description of particular embodiments of the present invention isnow complete. Many of the described features may be substituted, alteredor omitted without departing from the scope of the invention. Forexample, in a disclosed embodiment, the LO1 and LO2 signals are providedto a series of slave converters in a daisy-chain arrangement. However,if delay in the LO1 and LO2 signals becomes significant in a particularapplication, the slave connectors can be arranged in a starconfiguration, equalizing the electrical path lengths to each slaveconverter, as is shown for the reference connectors providing the R1 andR2 signals from the common reference signal generator 106 to the mastersynthesizer/receivers 102(1-N) in FIG. 1. Deviations from the particularembodiments shown will be apparent to those skilled in the art,particularly in view of the foregoing disclosure.

We claim:
 1. A signal conversion system comprising a first signalconverter, said first signal converter including: a first mixerincluding an input for receiving a signal to be converted; a secondmixer including an output for providing said converted signal; avariable oscillator for producing a signal (CS) variable at a firstscale; a splitter coupled to said first mixer and said second mixer toform a drift canceling loop, said splitter including an input coupled toreceive said signal (CS) from said variable oscillator, a first outputcoupled to introduce said signal (CS) into said drift canceling loopalong a first direction, and a second output coupled to introduce saidsignal (CS) into said drift canceling loop along a second directionopposite said first direction; a delay device coupled between saidsecond output of said splitter and an input of said second mixer; acomplementary delay device coupled between said first output of saidsplitter and an input of said first mixer, at least one of said delaydevice and said complementary delay device being adjustable; a slaveoutput coupled to provide a signal (LO1) from a second input of saidfirst mixer to a slave converter; and a second slave output coupled toprovide a signal (LO2) from an input of said second mixer to said slaveconverter.
 2. The signal conversion system of claim 1, furthercomprising: a second variable oscillator for producing a signal (FS)variable at a second scale finer than said first scale; and a thirdmixer coupled between said splitter and said first mixer and having aninput coupled to receive said signal (FS) from said second variableoscillator.
 3. The signal conversion system of claim 2, wherein: saidcomplementary delay device introduces an adjustable delay to signalspassing therethrough; and said delay device introduces a fixed delay tosignals passing therethrough.
 4. The signal conversion system of claim3, wherein: said delay device introduces a delay in one side of saiddrift canceling loop that exceeds by a predetermined amount a delay thatwould occur in an opposite side of said drift canceling loop withoutsaid complementary delay device; and said complementary delay device isadjustable over a range sufficient to balance the delays on both sidesof said drift canceling loop for a predetermined range of signalfrequencies.
 5. The signal conversion system of claim 4, furthercomprising a controller coupled to said complementary delay device andoperative to adjust said complementary delay device based at least inpart on a current frequency of said variable oscillator.
 6. The signalconversion system of claim 5, wherein said controller is operative toadjust said complementary delay device based at least in part on acurrent frequency of said second variable oscillator.
 7. The signalconversion system of claim 2, further comprising: a second signalconverter; and a reference signal generator coupled to simultaneouslyprovide a same reference signal (R2) to both said signal converter andsaid second signal converter.
 8. The signal conversion system of claim7, wherein said second signal converter comprises: a first mixerincluding an input for receiving a second signal to be converted; asecond mixer including an output for providing said converted secondsignal; a variable oscillator for producing a signal (CS2) variable at afirst scale; a splitter coupled to said first mixer and said secondmixer to form a drift canceling loop, said splitter including an inputcoupled to receive said signal (CS2) from said variable oscillator, afirst output coupled to introduce said signal (CS2) into said driftcanceling loop along a first direction, and a second output coupled tointroduce said signal (CS2) into said drift canceling loop along asecond direction opposite said first direction; a delay device coupledbetween said second output of said splitter and an input of said secondmixer; and a complementary delay device coupled between said firstoutput of said splitter and an input of said first mixer, at least oneof said delay device and said complementary delay device beingadjustable; a second variable oscillator for producing a signal (FS2)variable at a second scale finer than said first scale; and a thirdmixer coupled between said splitter and said first mixer and having aninput coupled to receive said signal (FS2) from said second variableoscillator.
 9. The signal conversion system of claim 8, wherein: saidsecond variable oscillator of said first signal converter is coupled toreceive said reference signal (R2) from said reference signal generatorand is configured to use said reference signal (R2) to generate saidsignal (FS); and said second variable oscillator of said second signalconverter is coupled to receive said reference signal (R2) from saidreference signal generator and is configured to use said referencesignal (R2) to generate said signal (FS2).
 10. The signal conversionsystem of claim 1, further comprising: a second variable oscillator forproducing a signal (FS) variable at a second scale finer than said firstscale; and a third mixer coupled between said splitter and said secondmixer and having an input coupled to receive said signal (FS) from saidsecond variable oscillator.
 11. The signal conversion system of claim10, wherein: said delay device introduces an adjustable delay to signalspassing therethrough; and said complementary delay device introduces afixed delay to signals passing therethrough.
 12. The signal conversionsystem of claim 11, wherein: said complementary delay device introducesa delay in one side of said drift canceling loop that exceeds by apredetermined amount a delay that would occur in an opposite side ofsaid drift canceling loop without said delay device; and said delaydevice is adjustable over a range sufficient to balance the delays onboth sides of said drift canceling loop for a predetermined range ofsignal frequencies.
 13. The signal conversion system of claim 12,further comprising a controller coupled to said delay device andoperative to adjust said delay device based at least in part on acurrent frequency of said variable oscillator.
 14. The signal conversionsystem of claim 13, wherein said controller is operative to adjust saiddelay device based at least in part on a current frequency of saidsecond variable oscillator.
 15. The signal conversion system of claim 2,further comprising: a second signal converter; and a reference signalgenerator coupled to simultaneously provide a same reference signal (R2)to both said signal converter and said second signal converter.
 16. Thesignal conversion system of claim 15, wherein said second signalconverter comprises: a first mixer including an input for receiving asecond signal to be converted; a second mixer including an output forproviding said converted second signal; a variable oscillator forproducing a signal (CS2) variable at a first scale; a splitter coupledto said first mixer and said second mixer to form a drift cancelingloop, said splitter including an input coupled to receive said signal(CS2) from said variable oscillator, a first output coupled to introducesaid signal (CS2) into said drift canceling loop along a firstdirection, and a second output coupled to introduce said signal (CS2)into said drift canceling loop along a second direction opposite saidfirst direction; a delay device coupled between said second output ofsaid splitter and an input of said second mixer; and a complementarydelay device coupled between said first output of said splitter and aninput of said first mixer, at least one of said delay device and saidcomplementary delay device being adjustable; a second variableoscillator for producing a signal (FS2) variable at a second scale finerthan said first scale; and a third mixer coupled between said splitterand said first mixer and having an input coupled to receive said signal(FS2) from said second variable oscillator.
 17. The signal conversionsystem of claim 16, wherein: said second variable oscillator of saidfirst signal converter is coupled to receive said reference signal (R2)from said reference signal generator and is configured to use saidreference signal (R2) to generate said signal (FS); and said secondvariable oscillator of said second signal converter is coupled toreceive said reference signal (R2) from said reference signal generatorand is configured to use said reference signal (R2) to generate saidsignal (FS2).
 18. The signal conversion system of claim 1, furthercomprising said slave converter, said slave converter including: a firstmixer including an input for receiving a second signal to be convertedand a second input coupled to said slave output of said first signalconverter; and a second mixer including an output for providing saidconverted second signal and an input coupled to said second slave outputof said first signal converter.
 19. The signal conversion system ofclaim 18, further comprising a plurality of said slave converters, eachof said slave converters including: a first mixer including an input forreceiving a respective signal to be converted and a second input coupledto receive said signal (LO1) from said slave output of said first signalconverter; and a second mixer including an output for providing saidrespective converted signal and an input coupled to receive said signal(LO2) from said second slave output of said first signal converter. 20.The signal conversion system of claim 18, further comprising: a secondsignal converter; and a reference signal generator coupled tosimultaneously provide a same reference signal (R2) to both said signalconverter and said second signal converter; and wherein said firstsignal converter additionally includes a second variable oscillator forproducing a signal (FS) variable at a second scale finer than said firstscale, said second variable oscillator coupled to receive said referencesignal (R2) and being configured to use said reference signal (R2) togenerate said signal (FS); and a third mixer coupled between saidsplitter and said first mixer and having an input coupled to receivesaid signal (FS) from said second variable oscillator; and said secondsignal converter includes a first mixer including an input for receivinga second signal to be converted; a second mixer including an output forproviding said converted second signal; a variable oscillator forproducing a signal (CS2) variable at a first scale; a splitter coupledto said first mixer and said second mixer to form a drift cancelingloop, said splitter including an input coupled to receive said signal(CS2) from said variable oscillator, a first output coupled to introducesaid signal (CS2) into said drift canceling loop along a firstdirection, and a second output coupled to introduce said signal (CS2)into said drift canceling loop along a second direction opposite saidfirst direction; a delay device coupled between said second output ofsaid splitter and an input of said second mixer; and a complementarydelay device coupled between said first output of said splitter and aninput of said first mixer, at least one of said delay device and saidcomplementary delay device being adjustable; a second variableoscillator for producing a signal (FS2) variable at a second scale finerthan said first scale, said second variable oscillator coupled toreceive said reference signal (R2) and being configured to use saidreference signal (R2) to generate said signal (FS2); and a third mixercoupled between said splitter and said first mixer and having an inputcoupled to receive said signal (FS2) from said second variableoscillator.